NBSIR 74-560

Stress Corrosion Behavior of Selected

Types of Stainless Steels and Titanium

Alloys in a Marine Environment

W. F. Gerhold and E. Escalante

Corrosion and Electrodeposition Section

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

August 1974

Twelve Year Progress Report

Prepared for Naval Air Systems Command

Department of the Navy

Washington, D. C. 20360

NBSIR 74-560

STRESS CORROSION BEHAVIOR OF SELECTED

TYPES OF STAINLESS STEELS AND TITANIUM

ALLOYS IN A MARINE ENVIRONMENT

W. F. Gerhold and E. Escalante

Corrosion and Electrodeposition Section

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

August 1974

Twelve Year Progress Report

Prepared for Naval Air Systems Command

Department of the Navy

Washington, D. C. 20360

U. S. DEPARTMENT OF COMMERCE, Frederick B. Dent. Secretary

NATIONAL BUREAU OF STANDARDS. Richard W. Roberts. Director

STRESS CORROSION BEHAVIOR OF SELECTED TYPES OF STAINLESS STEELS

AND TITANIUM ALLOYS IN A MARINE ATMOSPHERE

W. F. Gerhold and E. Escalante

REference: (a) Naval Air Systems Command (Bureau of Aeronautics)

Aer-AE-413/121 Letter dated 23 December 1958).

INTRODUCTION

A major problem encountered in the operation of aircraft at supersonic speeds is the aerodynamic heating caused by friction between air

and the external surfaces of the aircraft. At the high speeds such as are presently being encountered in certain military aircraft, this heating

is great enough to produce temperatures in excess of the safe operating

temperatures of certain aluminum alloys and other materials which had

formerly been used in airframe construction. In order to insure safe

operation at elevated temperatures, it became necessary to select materials

which were capable of retaining high strength at the temperature produced

by aerodynamic heating. Alternate materials were titanium base alloys,

austenitic stainless steels and tool steels.

One of the primary requirements for aircraft structural materials is

formability for the particular application involved. The materials must

have the necessary strength at both room temperature and elevated temperatures.

They must be in the softened condition for ease of fabrication and must

be capable of being hardened after fabrication to obtain higher strength.

The hardening treatment is often a limiting factor. Distortion in hardening,

excessive oxidation or pickling of formed parts may preclude the use of a material.

While high strength is of utmost importance, since tension as well

as compression strength is required over a wide temperature range for long

periods of time, the material must also be free of excessive embrittlement

have adequate corrosion resistance, and be insensitive to stress corrosion

cracking.
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Until recent years, the corabination of high strength, corrosion

resistance and good resistance to stress corrosion cracking in standard

chromium- nickel stainless steels could only be produced by cold working.

More recently, there has been developed a group of steels commonly called

age-hardening or precipitation-hardening stainless steels.

The vast majority of stress-corrosion literature is confined to

tests conducted in various aqueous solutions . For mechanistic studies

this approach is ideal. For more practical applications, actual environmental .^ti^d^es are more suitable and some studies have included atmospheric

tests, ' ' Recent failures in space vehicles has again brought to the

foref ront^t^e importance of studies that simulate actual operating con- ditions. '

Since relatively little information was known about the long-term

stress corrosion and corrosion behavior of these materials. Reference (a)

requested NBS to conduct tests in the marine atmosphere to determine their

corrosion and stress corrosion behavior. Included in this study also were

several titanium base alloys and a magnetically soft Fe-Al-Si alloy generally

used for electrical applications. This report contains the results obtained

for these materials after exposure in the marine atmosphere for up to

twelve years.

EXPERIt4ENTAL

All tests were conducted in the marine atmosphere at Kure Beach,

North Carolina (80-foot and the 800-foot stations). Specimens were

stressed by one of two methods, i.e., constant load (lever system) or constant strain (bent beam system).

From the standpoint of stress analysis the constant load lever

system is the simplest way to apply a load to the specimen. However, it

requires somewhat cumbersome and costly equipment. Stressing the specimen

a predetermined amount is simply a matter of obtaining the stress vs. strain characteristics of the material and then applying the desired load

to the specimen. The specimen is normally machined so that it has a reduced section where failure is most likely to occur.

In order to expose, a large number of stressed specimens in a given area at a minimum of expense, the constant strain, bent beam system was

used for sheet materials wherever possible. The distance between the two

constraining points (slots) on the specimen holder (jig) is a constant for

a given material and is dependent on the stiffness of the material. In
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this case determining the stress is somewhat more complicated. As before,

the stress-strain relationship is determined and from this the yield

strength is obtained. The approximate length of the specimen to produce the

desired stress for ^y^ig of fixed length is then calculated using methods

described elsewhere . A specimen is machined to this calculated length,

then placed in the jig where strain gages at the mid-point on the specimen

are used to determine the actual stress. Once the specimen length which

will give the desired stress is determined, a series of specimens are machined to various lengths. The stress for these specimens when placed

in the jig is determined using the same method described above. A curve can then be drawn by plotting strain vs. specimen length (Figure 1). From

this curve a specimen length can be selected which will produce the desired

stress on the specimen. Calibration curves of the type shown in Figure 3

were made for each alloy and thickness for materials to be stressed using

the bent-beam system. Typical curves for selected materials are shown in

Figures 2, 3 and 4. Specimens were originally cut from the sheet material

in strips l-l/8"x9". These were then further machined by removing 1/16"

(approximately) from each edge to a final width of 1"+ 0.001" such that

the edges were parallel to each other and the ends were normal to the edges

and parallel to each other. Burrs were removed from the edges by using

fine emery papers. Specimens were further machined by removing sufficient

material from one end of the specimen to give the length for the desired

stress.

All of the specimens were de greased in trichlorethylene, chemically

cleaned with inhibited phosphoric acid, rinsed in distilled water and air

dried. They were then heat treated in accordance with the treatments given

in Table 2.

Following heat treatment, the specimens were wet grit blasted to remove any oxides that might have formed during heat treatment. Specimens were then rinsed in distilled water and air dried. During the entire

specimen preparation procedure including loading and placement at the test

site, care was taken at all times to handle the specimens with clean gloves.

This procedure was carried out for all specimens in this study.

The predetermined stress was applied to the specimens just prior to

placing them on the exposure racks. In the case of the constant load lever

system, this was simply a matter of applying sufficient weight to the lever

arm. For the bent beam system the specimen had to be bent just enough to

allow it to be placed in the holder in its constrained position. For this

purpose a special adjustable tree-point jig was designed and built which

facilitated this process.
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MATERIALS

Two groups of materials were investigated and will be discussed

separately. The first group includes the ferrous alloys, while the second

group includes only the titanium base alloys.

Ferrous Alloys : Table 1 is a compilation of the ferrous alloys and

their nominal chemical compositions. All materials, in this table, except

for one, are of the age hardenable type. These materials can be classified

according to their more common metallurgical structures. The first includes

the austenitic stainless steels, A286 and HNM. Both of these alloys work

harden readily. However, their principal mode of strengthening is through

aging. Table 2 lists the heat treatment used for the ferrous alloys.

Neither alloy is prone to over-aging as evidenced by the higher temperature

and longer time used for precipitation hardening.

The second includes the semiaustenitic alloys. They are referred

to as semiaustenitic because of their dual structure which is austenitic

in the annealed condition and martensitic in the hardened condition. As a whole, their heat treatment is more complicated since some of these alloys

derive their strength through martensitic transformation which may involve

sub cooling or cold work plus some age hardening treatment or some combination

of these. AM 350 is an example of an alloy where three completely different

heat treatments have been used for hardening.

The third is the martensitic stainless steels which as their name implies derive their strength from a martensitic transformation on cooling.

Additional heat treatment through aging increases the strength of these

alloys.

The fourth in this group of ferrous alloys is made up of the one alloy which is not a precipitation hardenable stainless steel but is valuable

because of its resistance to high temperature oxidation. This is called

modified thermenol and its high resistivity and low oxidation characteristics

make it valuable for electrical applications.

Titanium Alloys ; The nominal composition and heat treatment of the

titanium base alloys are given in Table 3. These alloys are subdivided

according to the crystal structure.

The first is a single phase, alpha type alloy having a hexagonal

structure. It is the AllO AT titanium alloy which is not hardenable by

heat treatment. To increase its strength this alloy is normally hot

rolled and then stress relieved. Forming is done above room temperature.
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Two-phase, alpha-beta type alloys comprise the second subdivision

in Table 3. The second phase, beta, imparts some beneficial characteristics

to these materials. Being body centered cubic, the beta phase allows

limited cold forming to be carried out. When the alloy is solution heat

treated and quenched, subsequent aging treatments increase its strength.

The last is titanium alloy B120 VGA which has an all-beta type

structure. This beta is meta-stable at room temperature and, thus, lends

itself to heat treatment. The alloy has outstanding cold forming characteristics. This alloy is normally used in a solution heat treated and aged

condition.

RESULTS

Stress Corrosion Behavior - Distance from Shore

A portion of the recent results of this study obtained at 75% of

the yield strength are listed in Table 4. Data is given in this table for

the two sites (80- foot and the 800-foot from the ocean at Kure Beach, North

Carolina). This work is still continuing for these specimens listed as not having failed, unless otherwise specified.

Both precipitation hardening austenitic stainless steels have shown

excellent resistance to stress corrosion cracking. No failures have been

observed in almost thirteen years of exposure. This^i^ ^^^agreement with

other published reports for this class of materials ' ' . Distance

from shore has no effect on its susceptibility to failure as can be seen in

the table. It is pertinent to point out that both austenitic alloys in this

study were fairly low strength and were not cold worked after solution heat

treatment. Strength was obtained through precipitation hardening.

The semiaustenitic precipitation hardening stainless steels are quite variable in their stress corrosion behavior when stressed to 75% of

their yield strength. PH 14-8Mo in this group of alloys stands out as the one material in which no failures occurred when in a CH 1050 condition. On

the other hand, all specimens of the 17Cr-5Ni foil failed within 13 days

whether cold rolled or cold rolled and aged. However, because special

loading equipment was needed for this material, it was only exposed in the

80-foot lot. The other materials fall somewhere between these two extremes.

The effect of distance was more evident in this class of alloys and without

exception the susceptibility to failure decreased as the exposure distance

from the water's edge increased. AM 355 DA and PH 15-7Mo CH 900 are two
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examples of this effect. In both cases specimens stressed to 75% of their

yield strength failed in the 80-foot lot, whereas not one specimen failed

in the 800-foot lot. This same situation reoccurs, though not as pronounced, in other alloy systems in this group such as AM 350 CR and 17-7

PH.

The third classification of ferrous alloys in Table 4 is the martensitic

precipitation hardening stainless steels. The three alloys studied are 17-4PH, C450 and C455., none of which have shown any susceptibility to

failure when stressed to 75% of their yield strength in this marine environment .

Of the three materials, only 17-4 PH has been on exposure for the

full thirteen years. C450 and C455 have been on exposure for three years.

Effect of Heat Treatment

Heat treatment can have a verVggreat effect on a material's susceptibility to stress corrosion cracking . Table 5 includes the materials and

their heat treated condition which is described in greater detail in Table

2. The column on the extreme right of Table 5 tabulates the percent failure

rate for each material. With this figure we can compare not only the effect

of heat treatment on a given material, but also relative performance between

alloys

The austenitic precipitation hardening stainless steels display

excellent resistance to failure in the solution treated and aged condition.

Aging was done at 1350°F.

AM 350 in the semi aus teni tic group of the precipitation hardening

stainless steels responded favorably to the double aging treatment. Only

one specimen in twenty failed in the double aged condition, whereas 95 to

100% of the specimens failed in the CR and SCT condition. Double aging

improved the resistance to failure of AM 355, but not enough to make it

significant. Its failure rate remained above 75%. PH 14-8Mo was completely

resistant to failure in the cold rolled and tempered condition while 55% of

the specimens given the subcooling and aging treatment failed under the same conditions. Six heat treatments were used on the PH 15-7Mo alloy.

Two of the six, TH 1050 and CH 900, had a failure rate of 80% and 65%

respectively. Figure 4 graphically displays the rate of failure versus tempering temperature of the remaining four heat treatments involving subcooling and tempering. Increasing the tempering temperature from 950° to

1100° F reduced the susceptibility to failure by better than two orders of
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magnitude, but even at best the failure rate Is still 60%. The 17Cr-5Nl

foil had a failure rate of 100% in both the cold rolled and cold rolled and

aged conditions o 17-7 PH was treated in the same manner as PH 15-7Mo. The

response, however, was different. The TH 1050 was only slightly better

than the CH 900 treatment. Neither had a failure rate greater than 45% as shown in Table 5. Sub cooling and tempering markedly improved the alloys'

stress corrosion resistance. Figure 4 is an illustration of this effect.

Notice that tempering at 1075°F or above reduced the failure rate to zero in the marine environment.

There were no failures of the martensitic alloys during the entire

period. All three heat treatments given the 17-4 PH stainless steel were

outstanding in their resistance to failure. C450 and C455 alloys in the

hardened condition also have displayed resistance to failure in the exposure

times shown. These materials, along with others that have not failed, are still exposed at Kure Beach.

Modified thermenol, heat treated for improved ductility, had a failure rate over 69% in both the transverse and longitudinal direction.

At least 60% of these failures were attributed to exfoliation rather than

stress corrosion. The exfoliation occurred in those specimens exposed for

the longer periods of time.

Effect of Stress Level

It is well established^ that the tendency for stress corrosion increases

with increasing stress level . In determining how much stress a material

can sustain in an environment without failure and within a given length of

time, threshold stress is often used. This has been defined by Logan as "the stress to which specimens may be subjected without .failure for a specified exposure period in the corrosive environment" . Figure 5 is an example of the distribution of data on a stress vs. failure time curve

for PH 14-8MO. No failures occurred in specimens stressed to 50% of the

yield strength, and only one specimen failed when stressed at 75% of the

yield strength. The threshold stress for this instance is something above

50% but less than 75% of the Y.S. The choice is an average of the two or 62.5% of the yield strength. Figure 6 is a similar curve of the data

obtained for three heat treatments for PH 15-7Mo. It may be seen that in

the CH 900 condition specimens did not begin to fail until practically all

specimens in the RH 10 75 condition had failed. The first failure of

specimens stressed at 50% of the yield strength and exposed in the CH 900

condition did not occur for almost six years. A compilation of the threshold

stresses under the conditions of this study is listed in Table 6. Where no failures occurred on specimens stressed up to and including 100% of the
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yield strength, the threshold stress is listed as greater than 100% of the

yield strength of the material. Conversely, if even one specimen failed at

50% of the yield strength, the threshold is stated as being less than 50% of

the yield strength.

Visual and Metallographic

The general surface appearance of all specimens was good considering

the length of exposure. Specimens exposed over ten years now have developed

a surface tranish or at most a very thin but visible layer of rust.

Visual inspection of failures reveals that essentially all failures

originated at an edge, or in a very few cases at pits or other surface

imperfections. Two distinct patterns were observed. In one case cracks

traversed directly across the specimen along a line perpendicular to its

sides. In the second case cracks originated at areas perpendicular to a side but then curved away from their original direction. These patterns

were characteristic within any given material. However, no relationship was found between the visual crack pattern to other characteristics of the

material such as strength, hardness, and crack type (i.e., transgranular

or intergranular)

Metallographic examination of the alloys revealed somewhat complex

structures typical of multiphase materials. On a few occasions this made

it difficult to get good grain boundary definition through normal etching

techniques. In general grains were small and equiaxed having an average

ASTM grain size of 10, The crack path was found to follow a combination of

transgranular and intergranular directions with one type generally predominating over the other.

The following results are typical of the metallographic information

obtained for these alloys;

It was found that AM 350-SCT stressed to 90% of its yield strength

failed intergranularly as shown in Figure 5a. The same alloy in the double

aged condition (DA) failed through a mixture of transgranular and intergranular cracking as seen in Figure 5b. Note further the fine structure

within the grains which made examination difficult.

17-7 PH in the RH 950 condition also revealed a mixed mode of fracture

as seen in Figure 6a, The ferrite phase is visible in this micrograph.

As the tempering temperature is increased to 1075°F this phase is no longer visible as shown in Figure 6b. The f erriti^reverts to austenite as the tempering temperature is raised above 1050°F . Also shown in this

micrograph are cube shaped titanium nitride inclusions which were found

distributed throughout the alloy.
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As mentioned above most failures in modified thermenol have been

attributed to exfoliation rather than stress corrosion. This form of

corrosion develops a blister- like appearance on the material with alternate

layers of corrosion product separated by thin layers of thermenol making

up the blister.

Titanium Alloys

The titanium alloys have shown outstanding resistance to stress

corrosion cracking. There were no failures of specimens exposed for twelve

years in the marine atmosphere. Table 7 lists the alloys exposed at the

80-foot lot in Kure Beach, while Table 8 lists those at the 800-foot lot.
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Summary and Discussion

Since relatively little information was available concerning the

stress-corrosion behavior of age-hardening or precipitation-hardening

stainless steels in marine environments, NBS was requested by NASC to

conduct studies in the marine atmosphere with several alloys used or contemplated for use in air-frame construction. Other materials included

in these studies were several commercial titanium alloys and an Fe-Al-Si

alloy.

This report contains the results obtained for these materials after

exposure for up to twelve years in the 80-foot lot at Kure Beach, N. C.

It is important to point out that the atmosphere encountered in service

is a complex combination of normal atmospheric corrodents plus the chemical,

mechanical, and thermal conditions contributed by the aircraft itself

during manufacture and use. This must be kept in mind by both the

researcher and the engineer.

There is general agreement of -^e^u^tg ^^tween the data obtained in

this study and other published data » » » > ^ xhe few differences that

exist have been pointed out. Because this study was planned and implemented

in the early 1960's, developments in improved heat treatments and alloying

after that period are not included here. However, these are mentioned where

they are known. Also new testing techniques employing fracture mechanics

had not been fully developed at the time this study was initiated and were

therefore no part of the program. Moreover, since most of the materials

included in this program were thin sheet material, fracture mechanics

techniques could not have been readily adapted for use in this study.

The precipitation hardening stainless steels have demonstrated

excellent resistance to stress corrosion failure in this study. However,

their alloying content is higher and their strength is lower than that of

the other materials as seen in Tables 1 and 2. Alloy A-286 is useful up

to 1300°F,

Of the eight semiaus tenitic alloys studied, three have shown excellent

resistance to failure. AM 350 in the double aged condition is one of these

three alloys. In this work AM 355 has indicated somewhat inferior resistance

to failure. Recent work on improving its carbide distribution has developed

a heat treatment that is an improvement over that used in this study

This new full hard SCT 1000 treatment foj^AM 355 may, thus, make it comparable

to AM 350 DA and other resistant alloys . AM 357 in a CRT condition had

poor resistance in all phases of this exposure. It is interesting to note
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that the main difference between these alloys is that the chromium content

increases as one goes from AM 357 to 355 to 350. PH 14-8Mo and PH 15-7Mo are similar in composition but quite different in their susceptibility to

cracking. 14-8Mo in the CH 1050 condition is one of the three alloys

mentioned as having excellent resistance to failure. Conversely, 17Cr-5Ni

was almost as prone to failure as AM 357. 17-7 PH was very good in conditions

RH 1075 and RH 1100, and particularly resistant to cracking in the latter

condition as no failures were noted in thirteen years. Other workers

have indicated that PH 15-7Mo is more resistant to stress corrosion than

17-7 PH even though the stress corrosion stress^^ntensity threshold, K-j-^^^,

they determined is the same for both materials . Our own findings

clearly indicate that 17-7 PH RH 1100 is superior to all heat treatments

of PH 15-7Mo studied. Correlation with their work is complicated because

it is not clear what environment they used for their smooth specimens.

The precipitation hardening martensitic stainless steels have shown

complete resistance to cracking. 17-4 PH had not failed in any of the four

conditions studied in thirteen years. C450 and C455 have had no failures

in the two years of exposure. Titanium and titanium alloys have been

reported to stress crack in the laboratory at elevated temperatures when

subjected to stress, ^^ove the yield point in the presence of chlorides in one form or another . Other laboratory studies have successfully ,jgused

cracking in methanol vapors with no detectable presence of chlorides

These studies serve as a caution that under some very special conditions

titanium alloys can fail by stress corrosion cracking. The atmospheric

work reported here has produced no failures in the entire time of exposure.

This is further supported by the fact that there have been no known failures

of these alloys in service.

REFERENCES

1. Latanison, R. M., and Staehle, R. W., "Stress Corrosion Cracking of

Iron-Nickel -Chromium Alloys" (Review). Proc. Conf. Fundamental Aspects

of Stress Corrosion Cracking, Ohio State University, 1967, p. 214.

2. Slunder, C. J., "Stress-Corrosion Cracking of High Strength Stainless

Steels in Atmospheric Environments," DMIC Report 158 (September 15,

1961).

3. Phelps, E. H., and Loginow, A. W., "Stress Corrosion of Steels for

Aircraft and Missiles," Corrosion j_6, 325 (1960).

4. Bloom, F. K., "Stress Corrosion Cracking of Hardenable Stainless

Steels," Corrosion 11,, 315t (1955).

5. Williamson, J. G., "Stress Corrosion: Saturn V Fights Back,"

Materials Engineering 6£, 34 (1968).

6. Raymond, L., and Kendall, E. G., "Why Titan's Bolts Failed." Metal

Progress 93 (Jan.), 103 (1968).

7. "Stress Corrosion Testing Methods," Stress Corrosion Testing (ASTM

publication STP 425), p. 12, 1967.

8. Denhard, E. E., Jr., "Stress Corrosion Cracking of High Strength

Stainless Steels," (Review). Agard, Proc. Symp. Stress Corrosion

Cracking in Aircraft Structural Materials No. 18, 1967.

9. Logan, H. L., The Stress Corrosion of Metals , The Corrosion Monograph

Series (John Wiley & Sons, Inc., New York, 1966).

10. Burnett, H. C, Duff, R. H., and Vacher, H. C, "Identification of

Metallurgical Reactions and Their Effect on Mechanical Properties

of 17-7PH Stainless Steel." Journal of Research 66C (1962).
11. Astley, W., and Scott, J., "The Environment Encountered in Aircraft

Service," Agard, Proc. Symposium on the Engineering Practice to Avoid

Stress Corrosion Cracking No. 53, 1969.

12. Aggen, G. N., and Kal tenhanser, R. H., "Relationship between Metallurgical Structure and Properties of Precipitation Hardening Stainless Steel," Advances in the Technology of Stainless Steels and

Related Alloys (ASTM publication STP 369), 1963.

13. Williamson, J. G., "Stress Corrosion Studies of AM355 Stainless

Steel," NASA Technical Memorandum , NASA TM X-53317, 1965.

14. Carter, C. S., Farwick, D. G., Ross, A. M., and Uchida, J. M.,

"Stress Corrosion Properties of High Strength Precipitation Hardening

Stainless Stainless Steel," Corrosion 2J_ (1971).

15. Cotton, J. B., "Stress Corrosion of Titanium Alloys," Agard, Proc.

Symposium Stress Corrosion Cracking in Aircarft Structural Materials

No. 18, 1967. .. -/

16. Ambrose, J. R., and Kruger, J., "The Stress Corrosion of Titanium and

Ti 8A1-1M0-1V in Methanol Vapor," Corrosion Science 8, 119 (1968).
Table 1. Nominal chemical compositions

of ferrous alloys.

n 1 1 oy Lr 111 1*10 a 1 Mn Pi

ncoo 1 3 1 1 . b

UMM 1 Q1 oQ C y . b o . b

rtnoOU 1 0 . b 4

1

MrioOO It; c1 b . b

/I4

o0

A M "3 c; 7 Anob/ 1 /I

1

/I4 J DUI /I OM/-> 1 /I

1 4

oo <i . b

DUI C IfJIn rn 1 b- /nO 1 b7

/ 1 17Cr-5Ni 17 5 1 17-7PH 17 7 1 17-4PH 16.5 4 3

C450 15 6 1 1 C455 12 9 2

Modified

thermenol

3.5 16
Table 2. Heat treat/nent for the ferrous alloys.

Alloy' Condition

Solution or Condi tioning Treatment

Temp

op Time Transformation

Mechanical Properties

Treatment

tensile Yield I Strength Strength Elongation

Temp Time ksi ksi

Austeni tic

A286 STA \ ouu 1 nr Air cool 1 ooc 1 j^b 1 c1 0 hrs TCI 7

i b 1 .

T n7 A

i 0/ .4 23 HNM TH1350 2050 1/2 hr Air cool 1350 16 hrs 128.0 72.8 22.5

Semi-Austeni tic

nA 1710 10 min Air cool , 1375-2 hrs 850 2 hrs 176.8 145.2 10 1710 10 min Air cool, -100°F-3 850 3 hrs 203.8 158.6 8.7 OR 1 ybu 10 min Air cool, cold roll 30,4 850 3 hrs 232.2 231 .5 15.5

AM355 DA 1 / 1

1 0 mi n Ai r coo 1 , 1 ilb-L 2 hrs 193,8 1 59 .2 8.8

1 / i U 10 min Air cool, -luu T-i hrs 0 c n obO 3 hrs 214.0 "yen a

\ 64 .8 9.3

AM355 - Condition unknown - 375.0 -

1 re

\tn \- Cold roll 50% oUU oJ hrs OOD • b (its 1 .4 b .c

rn 1 4 ol lU o r\n 1 u J u 1700 1 hr Air cool , -100°F-8 hrs ^ 1050 1 hr 219.6 213.6 12.3

CH1050 Cold rolled at mill (Cond. C) 1 UbU 1 nr 7/10 7 C 7 b .3

DUrn 1 C 7Mn 1 D- /no n u Q c n 1 / DU 10 min Air cool , -100°F-8 hrs you 1 nr CHH .U 717 n Lie. .U

c0 KM 1 UjU 1 /oU 10 min Air cool, -100°F-8 hrs 1 UbU 1 hr 717 f! c\c .U 7nc n

<:Ub .U b .b DUI n7R Kn 1 U/0 1 7c;n

1 /bU 10 min Air cool, -100°F-8 hrs 1 U/b 1 hr C\JH .U 1 yy .u

a 7 b .3 RHllOO 1750 10 min Air cool, -100°F-8 hrs 1100 1 hr 195.0 190.0 7.5 TH1050 1400 1-1/2 hr Air cool, 50°-60°-l/2 hr b 1050 1- /2 hr 214,0 199.0 6.5

CH900 Cold rolled at mill 60% (Cond. C) 900 1 hr 256.0 190,0 7.5

17-7PH CR Cold rolled at mill*^ , 313.8 280.0

(wire) CRA Cold rolled and aged at mill 332.5 310.3

1 7-7PH RH95C 1750 IC min Air cool, -100°F-8 hrs 950 1 hr 227.0 214.0 7.2 RH1050 Air cool , -100°F-8 hrs 1050 1 hr 194.8 1 78.3 10 RH1075 Air cool, -100°F-8 hrs 1075 1 hr 185.1 170.3 10.3

RHllOO Air cool , -100°F-8 hrs 1100 1 hr 172.0 151 .8 11.5

TH1G50 1400 1-1/2 hr Air cool, 50°-60°-l/2 hr 1050 1-1/2 hr 189.9 175.3 . 8.7

CH900 Cold rolled at mill 60% (Cond. c) 900 1 hr 274.9 265 .7 11.5

17-7Ph CH^ . 0.020 diam wire 316.7

(wi re) CH^ 0.039 diam wi re 331.7

CH*^ . 0.055 diam wi re 320.8

CH° 0.120 diam wi re 301.8

Martensi tic

17-4PH TH925

D Col d rol led at mi 1 1 45% 925 4 hrs 184.7 180.2 3.8

17-4PH TH925 2150 1 hr Air cool, 1900°-1 hr^ 925 4 hrs 178.4 165,4 6.75

(forging) TH1025 2150 1 hr Air cool, 1900°-1 hr^ 1025 4 hrs 160.3 152.5 7.5 TH1025 2150 1 hr Air cool, 1900°-1 hr^ 1150 4 hrs 138.4 112.5 12

C450 Hardened 1900 1/2 hr

D Quench 900 4 hrs 179.2 172,0 11.1

C450 Hardened 1525 1/2 hr

D Quench 1000 4 hrs 225,5 219.8 8.7

Modified Thermenol

Transverse Rolled at 1070° 1340 1 hr° 151.6 1.0 Longi tudinal 135.2 123.8 1 .9

Sheet material unless otherwise specified.

As received.
Table 3. Nominal chemical composition of the

titanium base alloys.

Alloys Al V Other Condition Treatment

All OAT 5 1 2.5Sn HCR Hot rolled, annealed

C115VA 4 1 3Mo STA Soln H.T.,*^ 925°-12 hrs

C105VA 2.5 16' STA Soln H.T.,*^ 950°-4 hrs

Ti6A14V 6 4 STA Soln H.T., 950°-4 hrs*^

B120VCA 3 14 llCr STA Soln H.T.,^ 900°-48 hrs

^Sheet material

'^As received.
Table 4. Stress corrosion behavior of ferrous alloys stressed to 75%

of their yield strength at Kure Beach, N.C.

Alloy and

Condi tion ExposureStress

ksi

Stress

Di rectfon

80-ft Lot

Number of Specimens

Exposed Failed

Average

Time to Failure

(days)

800-ft Lot

Number of

Specimens

Average

Time to Fa i lure

(<Jays)

Exposed Failed

Exposure

Time of Unfailed

Specimens^

(years)

Austeni tic

A286 STA 80.6 5 0 NF« 5 0 NF 12.8

HNM TH1350 54.6 T 5 0 NF 5 0 NF 12.8

Semi-Austenitic

AM350 DA 108.9 T 5 0 NF 5 0 NF 12.8 SCT 119.0 T 5 5 19 5 5 104b

_ CR • 173.6 T 5 5 44' 5 3 96? 12.8 m2S5 DA 119.4 T 3 3 2863 3 0 NF 12.8

SCT 123.6 T 3 3 3 3 3 18 -

AM355 unknown .090 wire 280.0 T 3 3 241 _ .

AM357 CRT 211.4 T 5 5 3 5 5 3 PHU-SMo SRH1050 160.2 T 5 1 2536*' 5 0 NF 10.2

Vrffl I UDU t O i . O T

1 C3 U 11 r C3 u Mr

PH15-7M0 RH950 159.0 T 5 5 9 5 5 20 - RH1050 154.5 T 5 5 49 5 5 350 - RH1075 149.3 T 5 5 5 4 795" 12.8

RHi Km I 1

1 nnUU 1 *4c. . D T

1 c9

O

C ^ 1 OU c A

U fir TH1050 149.3 T 5 5 680 5 5 750 LMyuu 1 85 .£ T 5 5 2742 5 0 NF 12.8

i/Cr-5Ni CR 210,0 T 3 3 8

CPJ\ , 235.5 T 3 3 13 I I _

17-7PH Rli950 160.

T • 5 5 5 5 20 - RHI050 133.5 T 5 2 1 793 5 0 NF 12.8 RHllOO 114.

T 5 0 NF 5 0 NF 12.8 TH1050 131 .3 T 5 3 1966 5 0 NFu 12.8 CH900 199.5 T 5 5 707 5 2 1297^ 12.8

17-7PH CH .020 wirt^i 237.5 T 2 2 60

.039 wire*^ 248.

T 3 0 NF

.055 wire*^ 236.3 T 3 2 1614 9.9

.120 wire'i 227.2 T 3 3 532

Martensitic

17-4PH TH925 135.2 T 5 0 NF 5 0 NF 12.8

17-4PH TH925 forging 124.4 T 3 0 NF 3 0 NF 12.8 TH1025 forging 114.4 T 3 Q NF 3 0 NF 12.8 TH1150 forging 84.4 T 3 0 NF 3 0 NF 12.8

C450 hardened 129.0 T 5 0 NF 5 0 NF 2.3

C455 hardened 164.9 T 5 0 NF 5 0 NF 2.3

Modified thermenol

Transverse*^ 113.7 T 5 5 . 195 5 5 122 Longitudinal 92.9 L 4 2-(2£)^ 2383 4 3-(2£)^ 648 12.8

^Sheet material unless otherwise specified.

One or more spociriiens still on exposure.

'jSpecimens still under exposure unless otherwise specified.

Experiment ended at time shown. ^No failure. Transverse. ^Number of specimens failed by exfoliation. Stressed to % of tensile strength.
t/1 01 "O C «« t«- O OJ I/) 3 O — E iyl —

o 0* 'a o oj Q. E aj X — = Q.- uj :u t/1

< f- u-

(LI O O) Oi *-> i- —

I- o ^ >> > -t- <0 T3

QJ E 'O

(/I

1/1 *^

o -oc — o

o o

00 CO 00 CO CO

<NJ C^g CM CM C\J

m kt* m in ^

uf) m co un un

Ps* r«* CO *^ IT) <M ^ fO OJ — *— n r— LO

m in lo

i/> in in m (r> m

0% O O O <M ^ CM O CO ^ rsj ^ vo

iA LO m <M m

(/) tn m ui m in

in «j- u_ u_ «r u. ^ := z: -g- z

CO 03 CO GO CO

rsj CM CM evj CM

f*si Ln a\ CO

C3 u- u- m ^ = z *— CM

in in o o CO m

in tn in in in in

CO CO CO

CM OJ CSJ

CO 00

fVJ CM

coo^ co»— rjcn

r>.r*-u_.— <T> oinr^co

HZ CO f cn *—

n m in ^ o cn m

m in in m m m

CO *n *n esj

m ro m CM

o I o o o O

in m n in in

. Lu. Llo o o o o o

in ro cn <n in in

1 m in f** o 1- I- (M

;r z C3^ m >— — a* o>

» m in CM o o rn in

m in in m m m

z z z z in

m r-> o O ^ O mm tnoooocsi

m m in in in in m m in in in m

CM o CM ro

CM CO cn cn

</i t/t CO k U VD

in >v >>o>

CM

CO o> m o O

CO d c^

o o o o o o

in fo CO ro in in

CM CM

o o o o o o

V m ro m in in

m o o in — o O in moo CT. ^ —

ca£ Qc: ac t—

X 2 X 3 o in o CM m in CM oo oinoo o o o — omo o^nf^oino .... ^oo inoo'-oo ^ — <t — '— — — o\

CC CC C£. C£.\— <_> < ^

U t/1 I/) a> o o

Q. CX<—

trt X c

O tn V E

(U fl» -a *-» £ c C -.- 3

3 (_> "a « in c

C OP 3 i- O -3

in 01 in o

4J O •— W ItJ

Q) 0} ^ a. £ C Q. X O

<n o m uj z

lO ^ u 01 ^

c -3 y U E i- I— Z 1/1
Table 6. Threshold stress of ferrous alloys exposed at the 80-foot lot in Kure Beach, North Carolina.

Alloy^ Condition . ^ield ksi Unfailed

^ Strength Specimens

(years)

Threshold Stress, Oj Exposure

Time to

A286 STA >100 >107.4 12.8

HNM TH1350 >100 > 72.8 12.8

HrioDU /o<ay<yu

102.9-130.7

%120

• SCT

CR <50

<50

<79.3

<115.7 12.8

AM355 DA

SCT

50<C>r<75 <50 100 ^ 82.4

12.8

AM355 .090 wire <50 <187.5 11.3^

AM357 CRT <50 <140.7

PH14-8MO SRH1050

CH1050

50<OT<75

>100

-vl33.5 >242.410.2

10.2

PH15-7MO RH950

RH1050

RH1075

RHllOO

TH1050

CH900

<50

<50

50<aT.<75 50<o'<75

<50

50<o^<75

<106

<103

-^124

-viig < 99.5

12.8

12.8

12.8

12.8

12.8

17Cr-5Ni CRCRA

<50

<50

<140

<155.1 -

17-7PH RH950

RH1050

RH1075

RHllOO

TH1050

CH900

<50

50<o,<75

75<a;<90

>ibo

50<m-<75

<50

<107

-^140 >151.8

-vllO <132.8

12.8

12.8

12.8

12.8

12.8

17-7PH .020 .039

.055 .120

wire^ CH wire CH wire^ CH wire CH<50

75<a7<90

50<cTi-<75 <50

<158.3

•v274

'>200

- <151

9.9b

9.9'>

17-4PH TH925 >100 >180.2 12.8

17-4PH (forging) TH925

(forging) TH1025

(forging) THllSO

>100

>100

>100

>165.4

>152.5

>112.5

12.8

12.8

12.8

C450 Hardened >100 >172.0 2.3

C455 Hardened >100 >219.8 2.3

Modified Therinenol

Transverse'' Longitudinal

<50

<50 <61.9

12.8

12.8

^heet material unless otherv/ise specified,

^xperinent ended at tirre shov;n. jjStressed to of tensile strength.

Specimens still on exposure unless otherv/ise specified.
— -u »«

•r- to

T3 C -~

a> oj 1/t

I r- E I. — — (O

J *o u QJ>> UJ t— O (/)

01 o V

L —

cnc

!y > — o -o

1. •t H- U.

*jCO

•ou

>- U- i/l •o O C u.

01 o t- E

(U

J-? ^ o o o E 01 0) 3 Q. */» Z (/I o

a. Ex

1. 0) — >, > <o "O

«t 1— Lu—

> >- ITS -a < h- U- '

0> -M s.

>.•- O T3 p— C

•— o

«C < ce I— f- X I/) I/)

I- <t «t o Lf) in — — o

OJ 0) o> «/)

-c t. o a.

CO 1— a: oo

n3 ^ u "O
Table 8. Stress corrosion behavior of titanium alloys stressed

to 75% of their yield strength at the 800-foot lot

in Kure Beach, North Carolina.

a Alloy and

Condition

Exposure

Stress

ksi

Stress

Direction

Number of Specimens

Exposed Failed

Average

Time to

Failure

(days)

All OAT HRA 93.2

b

T 5 0 NF

C115VA STA 129.5 T 5 0 NF

C105VA STA 130.8 T 5 0 NF

Ti6A14V STA 131 .3 T 5 0 NF

B120VCA STA 132.8 T 5 0 NF

j^Sheet material

Transverse.

No failure.
Ul / Uj NlVdlS
o

o

o

00 o

CO o oCVI H19N3dlS an3IA dO % *SS3dlS
75 7o OF THE

YIELD STRENGTH

A

)l I I I I . 800 900 1000 1100 1200

TEMPERING TEMP,, °F

FIGURE 3. Stress corrosion behavior of PH 15-7 Mo - RH

and 17-7 PH - RH as a function of tempering

temperature


COs

a

•HO

<Ua.

CO

0)

CO

(U

4-t •H

QJ pjcu H CO

Co Co 3

iH M CO Oh O

CO C3 t d) 50 U CO

CO 4-t d (30 M

c^ C dJ •H >

4-i ^ (U

CU M

Tj

Ch S <U

CO (U CO U CO

i-i CO iH

13 4-J CU

4-1 cO CO H cO M

00 >-i M t>> d) (U O ^ 4J 1—

r-t C 1—1 d)

. 1 •ri CO rC

4-1 xs CO JJ •H 4J o rC CO

4-1 4J

UJ *H

o

4-) LO O cO X! • Xi O CO O

o

in CU o

4-1 4-i O

CO vO

1 c

o fa o •H

rH o •H .H •H 4-t CO

CO 4-t •rH CO •H X) -a

rc 13 0) ti x: o fa o o o

o 4-1 o

1 w m o

o

Ln O On O

iH o M-l dJ u-l O CO 0 X

CO O

CO 5-1 oo

dJ 0) Cu (U U-l O

d 4J OJ 4-1 4J 4J d) 1 O C! •H CU CO fa 3 •H )-l •H CO M u ai

4-J <u pd (-1 CO P-. u

o d) U d) •H O 1 1 a

o CO 4-1 id r-l rH •H w

/—

vO CO ^—
NBS.n4A (REV. 7-73>

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR RHFORT NO.

JiBSIR 74-560

2. Gov't Accession

No.

4. TITLE AND SUBTITLE

Stress Corrosion Behavior of Selected Types of Stainless

Steels and Titanium Alloys in a Marine Environment

3. Recipient's Accession No.

5. Publication Date August 1974

6. Performing Organization Code

7. AUTHOR(S)

W. F. Gerhold and E. Escalante

8. Performing Organ. Report No. NBSIR 74-560

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON. D.C. 20234

10. Project/Task/Work Unit No. 31P0410

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Naval Air Systems Command

Department of the Navy

Washington, D.C. 20360

13. Type of Report & Period

Covered jwelve year

Progress Report

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less [actual summary of most significant iriformation. If document includes a significant

bibliography or literature survey, mention it here.)

Stress corrosion data are presented for selected stainless steels and titanium alloys

exposed for up to twelve years in a marine atmosphere environment. Of the ferrous

materials included in this study, all except one were of the age hardenable type.

Variables studied included the effect of heat treatment applied stress.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicoJona)

Atmosphere; heat treatment; marine; stainless steels; stress corrosion; threshold stresd;

titanium alloys

19. SECURITY CLASS

(THIS REPORT)

UNCL ASSIFIED

21. NO. OF PAGES

29

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

22. Price

18. AVAILABILITY Unlimited

DT"' For Official Distribution. Do Not Release to NTIS

(

' Order From Sup. of Doc, U.S. Government Printing Office Washington, D.C. 20402, SD Cat. No. CI ^

I

' Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

USCOMM.OC 2e042.P74